I am replying as someone who spent and still spends a lot of time looking and considering, however for more hands on there are plenty of decent people here:
1) I was initially looking at coupe's but took out a stunning looking ragtop recently just to test out the sport shift and it kind of changed my mind. For an identical year/spec/mileage car, what kind of premium are you typically looking at paying for a roadster over a coupe? Same question for a sport shift over a manual. anything to look out for with earlier roadsters? or coupe's?
Around this time I am not sure there is a premium for a ragtop compared to a coupe, however if you wait until May June I am sure there is.
I think the sportshift has more of a premium than the manual, although I think it is definitely something to try as from my dealings with it the sportshift is rather like marmite - you either love it or hate it.
2) As far as resale values are concerned, what type would typically hold the value better e.g manual coupe vs. roadster/sport shift etc. What are considered essential options? (Ignoring trying to sell a roadster on a sunny day in May versus a wet day in November and buying a bright yellow car etc etc).
I think most people like the usual: satnav (even though most still use a TomTom), heated seats, premium audio, parking sensors. To be honest a lot of the earlier cars I have found are generally well specced, the only difference being more specialist things like stone guards. I hear a good premium is the sports pack (wheels and suspension I believe), but again this is personal preference as it does make it a bit harsher (depending on your back

).
3) Again, probably how long Is a piece of string, but for both sport shift and manual what is a ballpark figure for clutch life in terms of mileage (I understand this figure will vary massively). But on a hypothetical 40k mileage car... What would you be thinking? What would you be looking out for if buying one of these?
Ah, I think this depends on how you drive it. I have heard people get up to 50k out of them some 10k, I believe the average is around 30k.
4) If buying from a dealer, what are they typically willing to throw into the deal as far as sweeteners go e.g extending warranties, free servicing, etc. If I buy a car on relatively high miles on the first clutch is anybody going to throw me a 2 year warranty that covers a clutch as well if I push hard enough or is he just going to laugh me out of the showroom?
I think this depends on the dealer. Some dealers are not willing to even throw in a free pen (although they do usually extend to free tea or coffee), others are okay with giving a year's servicing or extended warranty, or something if you want a different coloured panel on the door. I have never heard of 2 years servicing but if you manage that one on a used car then good on you. I tried the "will you pay for the clutch if it goes" before and the dealer said only if it goes in the next 14 days otherwise we would consider making a contribution in first 12 months but can't tell you how much.
5) Last one.. As you can probably guess, this is my first foray into buying something a bit special. Have quite unique (but not necessarily bad) circumstances so lot of insurers are struggling to give me a quote that's not absolutely silly. Spoke to Nowell Richards who put the details through to an underwriter who gave me a much better quote than anybody else but just wondering if anyone else had any recommendations as far as insurers go to see if I can knock a few more quid off??
Always best to shop around. I have heard good deals from actual "bog standard" insurers like Admiral. Usual thing though get a quote from a year and then move to another.
Hope that helps.
Grants book is very good as well so that is always a good investment especially if you are thinking of parting with £40k of your hard earned tax free money.

I am told to have an Aston is an experience you will never forget, so good luck in getting the one you want

Neil